Bone marrow transplantation has become an important treatment modality for children and adults with immunodeficiency disorders, aplastic anemia, or hematologic malignancies. Significant problems limiting the efficacy of this procedure are frequently encountered post BMT, including graft rejection, graft versus host disease, and relapse of the original malignancy. Successful BMT involves complex interactions between specific subsets of donor and host cells early in the post BMT engraftment. This proposal is designed to study the kinetics of "normal engraftment" and hematopoietic reconstitution following BMT. To accomplish this objective, the investigator developed an analytical system using the polymerase chain reaction to distinguish between cells of host and donor. Methods to detect the persistence of minimal residual disease following BMT have also been described. The applicant demonstrates in preliminary studies the utility of this approach to perform quantitative engraftment analysis on small numbers of cells to document graft rejection and mixed chimeras. Using RNA PCR, it is possible to detect BCR/Abl transcripts unique to chronic myelogenous leukemia cells. The applicant has demonstrated persistence of tumor cells in some patients, despite the absence of clinical disease following allogenic bone marrow transplant. This application will utilize PCR genotype analysis to define the time course and completeness of engraftment of the lympho hematopoietic system following allogenic bone marrow transplantation. PCR analysis will also be used to determine the genotype and effect of ablative regimens on hematopoietic accessory cell subsets necessary for engraftment. RNA PCR will be used to detect minimal residual disease after bone marrow transplantation for CML, and a similar technique will address the utility of the Dexter-type bone marrow culture system to eliminate CML clones prior to autologous marrow re infusion. PCR assay systems are being developed to detect minimal residual disease in acute lymphocytic leukemia and non-Hodgkin's lymphoma. Finally, the number of stem cell clones needed for complete hematopoietic reconstitution will be determined using a quantitative RNA PCR assay to detect sequence polymorphisms within constitutively expressed X chromosome genes.